1. Field of the Invention
The present invention relates to a shift control method of an automatic transmission and a shift control system thereof. More particularly, the present invention relates to a shift control method of an automatic transmission and a shift control system thereof that improves responsiveness to a kick-down shift.
2. Description of Related Art
Generally, one friction element is released and another friction element is engaged according to clutch-to-clutch shift control. In this case, the slope of a turbine speed is controlled by means of hydraulic pressure of an off-going element, and thereby also is a shift.
As shown in FIG. 5, if a shift signal is detected, the hydraulic pressure of the off-going element is gradually increased after being quickly reduced such that the slope of the turbine speed is controlled. At this stage, hydraulic pressure of an on-coming element is maintained at a stand-by pressure after being pre-charged. After that, the hydraulic pressure of the off-going element is quickly reduced and the hydraulic pressure of the on-coming element is quickly increased to engaging pressure when a synchronizing point is reached, and thereby the shift is completed.
Meanwhile, during a specific skip-shifting process, two frictional elements may be released and two other frictional elements may be engaged. However, it is understood that shift control releasing two frictional elements and engaging two other frictional elements is difficult to be realized.
Therefore, much research into a situation in which two easily controllable shifting processes are successively preformed in the case of a skip shift has been conducted. That is, after a first shift where one off-going element is released and one on-coming element is engaged is completed, a second shift where another off-going element is released and another on-coming element is engaged is performed.
However, since two shifting processes are successively performed, the shifting time may be long and the shift feel may be deteriorated. Since the second shift is performed by means of the hydraulic pressure of the second off-going element after the first shift is performed by means of the hydraulic pressure of the first off-going element, shift time may be retarded and shift responsiveness may be deteriorated.
To solve such problems, many shift control methods of an automatic transmission where first and second shifts are overlapped have been researched. However, in a case in which many shift processes are overlapped, such as a shift from an eighth forward speed to a second forward speed, the shift time may be long and shift responsiveness may be deteriorated even if the shift is performed according to such a shift control method.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.